This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This grant explores the effect of oral contraceptives on body weight control in adulthood. Many women stop taking oral contraceptives because they are concerned about a perceived side effect, weight gain. But this failure to consistently take oral contraceptives leads to increased rates of unintended pregnancy. Surprisingly, studies in animals (mice, rats, cats, dogs, monkeys) have shown that estrogen and progesterone administration to ovariectomized animals generally leads to weight loss, rather than weight gain. The overall goal of this grant is to document changes in body weight when ovary-intact primates are chronically given oral contraceptives(OC) for a one-year period of time. We hypothesized that monkeys taking oral contraceptives for a yearmay in fact experience a mild weight loss;a finding which would discredit the perceived side effect of oral contraceptives in causing weight gain. All monkeys completed the study protocol with no adverse events. A significant increase in metabolic rate, a decrease in body weight, and a decrease in % body fat with pill use was found as compared to baseline. When analyzing the groups separately (obese versus normal), the obese group was responsible for the significant changes seen for the entire group.. No changes were seen in food intake, activity level, or % lean muscle mass with OC use for the entire group and for either BMI-based group. Overall, OC use appears to increase 24 hour metabolic rate in female monkeys, which in turn appears to differentially affect weight and % body fat depending on baseline weight.